Although Northern Ireland's politicians maintain the assembly elections will be about bread and butter issues, the decisive factor remains a single sectarian imperative: will a nationalist or unionist be elected first minister on 5 May?

Fears that Martin McGuinness could become Northern Ireland's first citizen are driving pro-union voters further into the arms of the Democratic Unionist party, veteran watchers of Ulster politics say.

DUP strategists have tapped into concerns that if McGuinness were elevated to first minister it would mark a psychological victory for republicanism and convince more unionists that a united Ireland was inevitable. In reality, whoever is elected first minister is meaningless in relation to Northern Ireland's place in the UK. But in the north of Ireland, perception and symbolism can be as important as reality.

Lord Bew, professor of politics at Queen's University Belfast, predicts that only about six seats will change hands this time. "Even if the issue of first minister is purely symbolic it will nevertheless play to the DUP's advantage. I am hearing that from their private polling the DUP are picking up the message that it is an issue for unionist voters," he said.

On the question of the DUP losing seats to the more hardline, anti-power-sharing, Traditional Unionist Voice, which in turn might enable Sinn Féin to become the largest party, Bew is sceptical. "Even if the DUP were to lose say three seats to the TUV they would still be on 33 seats overall and still marginally ahead of Sinn Féin. The only danger for the DUP and for all the parties is voter apathy. If they can get their electorate out they can hold their position as the number one party."

Sinn Féin leaders remain confident that they can pull further ahead of the SDLP in the battle within nationalism. In relation to the unionists, McGuinness has tried to avoid controversy over the first ministerial role, insisting it is irrelevant given that the post and that of deputy first minister are already on an equal footing.

But Tom Hartley, a veteran member of Belfast city council and close associate of the Sinn Féin president, Gerry Adams, admits that the campaign has been flat. "I never think it's wise for any politician to predict what the voters are going to do."

His party colleagues too are playing it cautiously, despite the fact that their comrades in the republic recently staged a stunning comeback in the Irish general election, securing 14 seats in the Dáil.

The two parties that have shipped most votes to their respective unionist and nationalist rivals claim that the issue of whoever takes the first minister post is not a burning issue on the doorstep.

Philip Robinson, 32, is standing for the Ulster Unionist party in East Belfast. A former press officer for David Trimble when he was first minister, Robinson insists that the UUP could add to its 18 seats, including winning one from the DUP in the east of the city.

Robinson (no relation to the first minister, Peter Robinson) says peace process issues have become more or less redundant now that the assembly has bedded down. "The people on the streets seem to be exercised by two main issues. The first is health and the survival of the NHS. And the second is the rising cost of living, particularly oil, petrol and gas. I think I encountered only one person so far on a doorstep who raised the question of who will be first minister after the elections."

One of the SDLP's rising stars also maintained that reports of his party's death, just like the UUP's, were grossly exaggerated. Conall McDevitt, who is half Irish and half Spanish, has been one of the SDLP's most energetic outgoing assembly members. He rejects the view that Sinn Féin will finally bury the SDLP.

He says there is "real disillusion" over what he calls the "DUP-Sinn Féin carve-up" of power, ministries and influence at Stormont. "No one has raised the question of who would be first minister during this campaign. Northern politicians are a lot more divided than the people are. Yes, there is apathy fuelled by bad politics. Many people just think Sinn Féin and the DUP want to do peace process politics and not real government. That said people do care about the assembly and want it working a lot better for them."

But the task for the smaller parties appears herculean. Even back in 1998 when the UUP was tearing itself apart over Trimble's decision to support the Good Friday agreement, the party still secured 28 seats in the first power-sharing assembly. But since then it has lost 10 seats to the DUP, with the latter party becoming the dominant force in unionism.

Overshadowing this six-week election campaign has been the return of terror and death to the streets of Omagh almost 13 years after the mass murder of 29 people in 1998.

The killing this month of the Catholic police officer Ronan Kerr resurrected fears of a return to full-scale terrorist violence. However, the outcry at the murder united Ireland, north and south. In particular it solidified the relationship between McGuinness and Peter Robinson, who put on a united front in their meeting with Kerr's family and later at his funeral. Bew said the "Sinn-Féin/DUP duopoly" had been strengthened.